On the similarities and differences between interface and abstract class in Java

Abstract classes and interfaces have puzzled me for a long time. In my opinion, interfaces are really similar to abstract classes. During this period, I also looked for many materials and referred to the opinions of various gods. I can only understand the difference between the two in grammar. Harden your head and make a small summary. Perhaps, after learning the knowledge, the understanding will be more profound, Ollie!

Grammatical differences

In depth understanding

abstract class People{
    private int age;
    public abstract void doSomething();
}

interface studyable {
    void howToStudy();

    default void info() {
        System.out.println("study is important for everyone..");
    }
}

public static void main(String[] args) {
    studyable[] studyables = new studyable[]{new Robot(),new Student()};
    for (studyable s : studyables) {
        s.howToStudy();
        s.info();
    }
    System.out.println("*************************************");
    People[] peoples = new People[]{new Student(),new Teacher()};
    for (People p : peoples) {
        p.doSomething();
    }

}

//测试结果
Robot comes out
Student comes out!
robot need to practice
study is important for everyone..
student will read book..
study is important for everyone..
*************************************
Student comes out!
Teacher comes out!
student should study..
teacher should teach..

Reference link: what is the difference between an interface and abstract class